3,6-disubstituted-1H-pyrazolo3,2-c!1,2,4!triazole couplers are important couplers for photographic products. They are, however, difficult to synthesize. Only a few practical synthetic methods to these couplers are known in the art. One of the preferred synthetic routes involves the preparation of the intermediate: 3,6-disubstituted-7H-1,2,4!triazolo3,4-b!1,3,4!thiadiazine(2). ##STR2##
The intermediate 2 can be prepared from the intermediate 1 (4-amino-5-mercapto-3-substituted 1,2,4!trizole), which is the subject of this invention, and an alpha-haloketone as illustrated by the following equation: ##STR3##
The intermediate compound 1 can be prepared according to Hans Beyer (Annalon der Chemie und Phamzie, 1960, 637, 135-145) and Westphal et al (Zeitschrift fur Chemie, 1969, 9, 111) by using thiocarbohydrazide and a carboxylic acid as follows: ##STR4##
This method uses no solvent. The two starting materials 4 and 5 were heated at a high (melting) temperature in their neat state. The described method suffers many disadvantages:
(1) This method is effective only when the carboxylic acid is liquid. The reaction can be very difficult if the carboxylic acid is a solid; PA1 (2) Thiocarbohydrazide 4 is an explosive and a highly hazardous material. A reaction operated at high temperature involving 4 without a solvent is very difficult because all the solid starting materials are not mixed evenly. As a result, local overheat could occur and explosion could result; PA1 (3) The reaction produces low yield of the intermediate 1 or no product at all. Extensive work-up is needed to obtain a reasonably pure final product.
A problem to be solved is to provide a safer low temperature process for preparing a 4-amino-5-mercapto-3-substituted-1,2,4!triazole.